1. Field of the Invention
This invention relates to a liquid-crystal display which can be used as direct-vision and projection type liquid-crystal displays.
2. Description of the Prior Art
Liquid-crystal displays have advantages, such as that they are small and thin and consume low power, and are used as displays for OA equipment and AV equipment.
The liquid-crystal display comprises a liquid-crystal panel which has a several-micrometer thick liquid-crystal layer filled between two transparent substrates which each have transparent electrodes, a driver circuit which supplies a signal voltage to the electrodes, and a light source which emits light to the liquid-crystal panel. An external input signal such as a video signal or an image signal from a computer is interfaced by the driver circuit and distributed to each electrode to apply voltage to the liquid crystal between the electrodes. Since the liquid crystal molecules have anisotropy in dielectric constant and refractive index, the application of voltage transforms original orientation state to the other state with different transmittance. For TVs and personal computer terminals, the monitors require picture elements in the range of from tens of thousands to several millions, so that the electrodes are minutely processed to arrange several hundred-micrometer picture elements in the form of a matrix and to apply different voltages to each picture element. Thus, the light and shade of each picture element are displayed to generate characters and images.
In addition to the application as a direct-vision type liquid-crystal display whose display screen can be seen by directly observing the liquid-crystal panel, the liquid-crystal display is also used as a projection type liquid-crystal display which is built into an optical system comprising a light source, a mirror and lenses as a projector. In the projection type liquid-crystal display, light emitted from the light source is given prescribed light and shade by the liquid-crystal panel and projected onto a screen to provide a large display. In particular, in widely used OHPs (overhead projectors), the use of the liquid-crystal panel instead of films eliminates problems such as the films needing to be changed by a presenter, and the images can be freely changed by a controller such as a keyboard.
The liquid-crystal display for OHPs is a projection type and does not have a light source. It is placed on the OHP's stage and modulates the light emitted from the light source of the OHP to throw a magnified image onto the screen. Therefore, this liquid-crystal display is dedicated for use with OHPs, and another display of a direct-vision type is required for the monitor of a personal computer when creating data. Although the OHP is not used so frequently, compared with the monitor, the liquid-crystal display for the OHP is required for presentation, so that users need separate displays dedicated for the monitor and the OHP, incurring high costs.